The present invention relates to a process for inserting points in a supporting mandrel made from a material able to receive the points by direct insertion under pressure, in order to form rows of points aligned in accordance with the generatrixes of the mandrel, as well as to a machine for performing this process.
In the production of bodies or members of revolutions made from three-dimensional material, it has already been proposed, more particularly in French Pat. No. 2,408,676, filed on Sept. 23, 1977 in the name of the Commissariat a l'Energie Atomique, to insert points in a mandrel so as to define between the said points longitudinal and circumferential passages and arranging in the latter, by winding and weaving, layers of superimposed wires, followed by the densification of the thus obtained assembly, e.g. by means of a thermosetting resin and finally the removal of the supporting mandrel. The thus obtained body or member comprises three rows of layers arranged in accordance with three preferred directions, which are optionally perpendicular to one another, the density of the wires in each of the three directions being as high as required. It is in this way possible to obtain a body of revolution made from a very thick three-dimensional material if the length of the points is adequate to permit the superimposing of numerous layers of wires on the mandrel by winding and weaving.
The principle of installing the wires in a substantially radial direction by the placing of pins on a mandrel covered with an easily penetrable layer and which can be removed after the layers of wires have been formed in two other directions is known from U.S. Pat. No. 3,577,294. However, in the latter the points are inserted by means of an air gap or the like which leads to a particularly imprecise insertion thereof. Thus, as soon as the density and particularly the length of the points increases, it becomes virtually impossible to produce layers of wires in two other directions as a result of the intersecting of the points. This is confirmed by the text of the aforementioned U.S. Patent, which clearly states that the points must be short and compares the structure of the mandrel after their insertion to that of velvet.
The aforementioned French Pat. No. 2,408,676 has already proposed a process and a machine using this principle. However, although the machine described therein is more accurate and therefore permits a finer insertion of the points to the mandrel, it still has certain technical limitations due to the fact that the distance between the surface to which the insertion is to be made and the guidance means of the points is entirely dependent on the length of the points to be inserted.
In the case of thick, three-dimensional pieces, in order to be able to carry out winding and weaving under normal conditions, the quality of the insertion of the points to the mandrel must be perfect. Thus, the fitted points must be perfectly aligned in accordance with the axis or in accordance with the circumference. This quality can only be obtained to the extent that the means used are very accurate. Thus, on considering a three-dimensional part, whose axial spacing is 3 mm, with a point length of 200 mm and a point diameter of 1 mm, a slight point deviation of 0.degree.34' during insertion would lead to the tips of the points touching, so that it would then be impossible to wind the same.
A critical analysis of the aforementioned processes and particularly that of French Pat. No. 2,408,676 of Sept. 23, 1977 reveals certain technical deficiencies or inadequacies. Thus, during its insertion in the foam the point must make room. Irregularities in the foam (bubbles, higher density, hard particles, etc) tend to deflect the point. Sectional and cross-sectional irregularities (point with a fibrous or bevelled cross-section) lead to faulty alignments of the points. Finally, surface irregularities (chips, protuberances, etc) damage the foam and overdimension the holes during the insertion process. The points then tend to drop very easily.
In addition, the straightness quality of the point must be increasingly high as the distance between the foam surface and the guidance members increases. The points, which are generally obtained from prepolymerized fibrous elements, have a slight prejudicial sag when the length reaches 50 mm or higher. With respect to the model made in the foam, insertion using such points is subject to serious irregularities. To obviate this deficiency, it is necessary to guide the point very accurately and design guidance means such that they do not prejudice the rest of the production cycle.
For the various reasons referred to hereinbefore, it is at present virtually impossible when using known processes to produce objects of revolution made from three-dimensional material having a thickness greater than 50 mm. However, for numerous insertions, it is desirable to have a process and a machine making it possible to insert points having a considerable length on a mandrel in order to subsequently produce objects of revolution made from a three-dimensional material having a significantly greater thickness and which can in fact reach 150 mm.